At the other end of the spectrum, your child may be totally uninterested in your pregnant belly. They may just not make the connection between your baby bump and a brother or sister at all.
The best advice is to wait until your child asks a question, and then to make the explanation as simple and short as possible. Ask your child what they think before you launch into a complex explanation. They may have a very simple query, and you explain far more than they ever wanted to find out.
Make sure that you use the correct terminology. Call genitalia by their proper name, and explain, for instance, that babies grow in a special place called a uterus, that only girls have. That avoids any confusion in boys in particular, when they wonder why they can’t grow babies in their tummies.
Explain the process of having a baby simply. Tell your child that the mummy and daddy make the baby together, and that the baby grows inside the mummy until it’s time to be born. That way, your child gets a grasp on the time frame involved in having babies.
Try not to be embarrassed, or treat sex or having babies as something that you shouldn’t talk about – your child will pick up on it, and that’s not a good thing!